The invention relates to an apparatus for the rotation of, for example, workpieces to be machined, on a carrier which can be set in rotation by a pinion shaft with toothed strips via a rack, the rack being arranged perpendicularly to an axis of the pinion shaft in a cylinder bore of a housing slidably between covers closing the cylinder bore, pistons provided on the rack at each end forming with a respective cover a chamber which can be subjected to pressure medium, and the toothed strips of the pinion shaft meshing with the toothing of the rack between the two pistons.
Rotary units of this type are known and are predominantly used for generating rotational movements, the rotational movements taking place only within a limited angle With rotary units of this type, in most. versions the rotational movements are generated as a result of the interaction of a rack and a pinion shaft. Preferably, a rack is guided between two pistons which form respectively between them and each of the covers closing the housing a chamber which can be subjected to a pressure medium. The pressure medium is controlled, for example, via proximity switches, by means of which the direction of rotation of the particular rotational movement is determined.
Since high dimensional accuracies are required for the machining of workpieces, it is necessary that a corresponding rotational movement be adjustable exactly in terms of the rotary angle. To guarantee such dimensional accuracy, most rotary units are equipped with corresponding devices determining the spacing between the toothed strip and the meshing pinion shaft. Thus, for example, there are known devices which by the use of two racks compensate a play which occurs under particular circumstances. Other devices provide under the rack a support bearing which is supported against the pinion shaft by means of appropriate spring devices or the like and which thereby compensates any play which occurs. The disadvantage of this device is that it either involves a high outlay or is exposed to increased wear as a result of the pressure force of the two toothing parts against one another.
Furthermore, in rotary units of this type, it is important that the end positions be reached in a damped manner. An abrupt break of the rotational movement leads to increased wear at those toothing points which are in engagement in the end positions, and because of the inertia of the workpiece it could result in the displacement of the latter, thus necessarily leading to an incorrect machining of this workpiece. To obtain such damped end positions, shock absorbers are introduced into the rotary units laterally in covers closing the pressure chambers and respectively damp the linear movement of the pistons in the region of the end positions.
The disadvantage of shock absorbers fastened in this way is that they can be sealed off only with great difficulty, and this repeatedly leads to pressure-reducing consequences within the chambers which can be subjected to pressure medium. Since the end positions of the rotational movement have to be varied according to the particular mode of machining of a workpiece, shock absorbers of this type cannot be installed unreleasably in the housing. A further problem is also presented by the size of such a rotary unit necessitated by the provision of such shock absorbers. Because the shock-absorber sleeves project on both sides, a rotary unit of this type often attains an undesirable constructional length.
Likewise, it is often shown to be a disadvantage of rotary units of this type that no intermediate position can be obtained between the end positions. But this is often necessary or would prove cost-effective in machining of a workpiece in which two work steps are required for the machining. With an appropriate intermediate position or within an appropriate intermediate stop, the two operations could be executed within one rotational movement.